The present invention relates to a tape carrier called a COF (Chip On Film) (hereinafter, referred to simply as COF) in which a semiconductor element is connected to and assembled on a flexible wiring substrate, and also concerns a manufacturing method for such a tape carrier and a manufacturing method for a package.
In a TCP (tape carrier package) in which semiconductor elements are continuously formed on a flexible wiring substrate, a through hole (hereinafter, referred to simply as a device hole) is preliminarily formed in a tape carrier member at a portion corresponding to a semiconductor element, and through this hole, a tip portion of a wiring pattern, which is referred to as an inner lead, and sticks out in a cantilever fashion, is connected to a semiconductor element electrode. The TCP has been widely used, for example, when a semiconductor element for driving a liquid crystal display is connected to the display panel.
In recent years, in the field of small and middle size liquid crystal panel devices, there have been increasing demands for both miniaturization of modules and large scale of liquid crystal panels. In order to meet these demands, a so-called packaging area, that is, a joining area between the liquid crystal panel and the TCP, needs to be reduced. However, in the case when the liquid crystal panel and the TCP are simply connected, a portion of the TCP other than the output terminal portion comes to protrude from the glass edge of the liquid crystal panel. When the amount of this protruding portion is large, the module becomes bulky, resulting in a reduction in the ratio of the panel display area to the module area. Therefore, in an attempt to reduce the amount of the protruding portion, a packaging method has come to be used in which the protruding portion of the TCP from the end of the liquid crystal panel is bent over to the rear face of the liquid crystal panel via the glass side face, as illustrated in FIG. 5.
Referring to FIG. 5, an explanation will be briefly given of the packaging sequence of the structure in which the TCP is bent over. In a liquid crystal panel constituted by an element side glass plate 13 and an opposing side glass plate 14, first, a terminal portion of the element side glass plate 13 and a film 16 constituting the TCP are joined to each other through an AC 15 (anisotropic conductive bonding agent), etc. In this case, since the film 16 other than the output terminal portion comes to protrude from the end of the element side glass plate 13, the protruding portion is bent over to the rear face via the side face of the element side glass plate 13. Next, a wiring pattern 4 on the TCP side, bent over to the rear face side of the element side glass plate 13, is connected to a connecting terminal section of a power-supply main substrate 18 with solder and a connector, etc. An IC chip 1 is placed on the film 16, and fixed thereon by resin 2, and the wiring pattern 4 and the film 16 have been bonded to each other with a bonding agent 17.
Here, as illustrated in FIGS. 6(a)-(c), in some arrangements, in order to miniaturize the power-supply main substrate 18, a part-placing area 9 is placed between the IC chip 1 and an input terminal section, and a resistor, a capacitor, etc. are placed on the TCP side of the power supply main substrate 18. FIG. 6(a) is a plan view of the liquid crystal panel showing a state of the TCP and the liquid crystal panel connected to each other, and FIGS. 6(b) and 6(c) are side views of the liquid crystal panel showing states before and after the bending process of the TCP.
Here, in the field of large-size liquid crystal panel devices, a number of TCPs need to be assembled in longitudinal and lateral directions of the liquid crystal panel so as to drive the liquid crystal panel. In this case, the TCP needs to be arranged not only to be simply bent over, but also to have a reduced stress that is exerted when bent over. Therefore, TCPs of another type have come to be used in which, illustrated in FIG. 5, cutout sections are preliminarily formed in the tape carrier member at portions corresponding to bending sections so that a stress exerted at the time of the bending process is reduced, and a cover coat is placed so that disconnection of the pattern at the bending portions is prevented.
The TCPs of this type make it possible to reduce the amount of the protruding portion of the TCP; however, the increased thickness of the bent over TCP results in an increase in the thickness of the liquid crystal module. Therefore, in the case when a thinner product is desired, another TCP structure which forms a flat packaging on the liquid crystal panel by using either the face-down packaging system shown FIG. 7 or the face-up packaging system shown in FIG. 8 is adopted. In FIGS. 7 and 8, a cover coat 3 and a wiring pattern 4 are stacked on the film 16, and an IC chip 1 and a wiring pattern 4 are connected by a connection lead 19.
In this manner, in the case when the flat TCP structure is formed on the liquid crystal panel, the thickness of the package is reduced by controlling the thickness of the IC chip 1, the forming depth of the connection lead 19 and the thickness of resin 2 so as to reduce the thickness of the package. Moreover, the package design is simply miniaturized so that the packaging area is reduced. However, problems such as a reduction in the strength against break arise, thereby giving a limitation to the attempt to reduce the IC chip 1. Thus, there have been demands for a thinner package which is bendable.
The COF has been developed to meet such demands by providing low cost products in which the functions of the TCP are limited. The COF is made of a thin film that is a thin film-shaped tape carrier material having a thickness of approximately 40 xcexcm. The COF has no device holes, and its wiring pattern to be joined to a semiconductor element electrode is lined with the tape carrier material.
Here, an explanation will be briefly given of processes for forming a generally used COF tape carrier.
First, a transport-use carrier tape is bonded to a film material with metal foil that has a two-layer structure formed into a thin film. Next, this is subjected to various processes, such as a resist-coating process, an exposing process, a developing process, an etching process and a resist-removing process, so that a pattern is formed on the metal foil. Further, among portions of the exposed metal foil pattern, resist is coated onto those exposed portions that are not connected to semiconductor element electrodes, etc. so as to be insulated. Lastly, the electrode connection sections of the metal foil pattern are subjected to a plating process so as to stabilize the connection between the metal foil pattern and the semiconductor element electrodes, etc.
As compared with the TCP, the features of the COF are that the formation process of the tape carrier is simple and that the material cost is inexpensive. Moreover, with respect to the COF, since its tape carrier material is inherently flexible, it is bendable at any portion except the peripheral portion of the assembled semiconductor element. Moreover, in the case of the application of a reinforcing film that adheres to the rear face of the tape carrier, it is possible to adopt a ultra-thin film having a thickness of 25 xcexcm.
Here, as compared with the TCP, the disadvantage of the COF is that, since the COF does not have a device hole on the film, the assembling direction of the semiconductor element is limited to the face-down direction as shown in FIG. 9. Therefore, the package design needs to be carried out on one plane, and in order to reduce the package area so as to cut costs and miniaturize the assembling area by reducing the tape carrier material, only the possible method is to improve the assembling efficiency by narrowing the wiring pattern and reducing the area of the semiconductor element. However, the improvement of the assembling efficiency depending on this method has reached a limit in terms of designing; therefore, the minimum package area required is inevitably determined, and the resulting problem is that it is no longer possible to reduce the package area to a great extent.
Moreover, even when a small package is achieved by package designing on one plane, the following problems might arise.
(1) When a part-placing area is placed on a small package, the intervals between the packaged parts become narrower, making it difficult to revise the parts, that is, making it difficult to repair or exchange the parts.
(2) In the case of a small package, since the joining area between the liquid crystal panel and the package becomes smaller, the joined portion is susceptible to peeling due to a stress occurring at the time of the package bending process, resulting in a disconnection. In order to solve the problem (2), one solution is to make the thin film further thinner so as to reduce the stress; however, to make the film thinner encounters a certain technical limitation. Moreover, when the film becomes too thin, the package tends to lose its flexibility, resulting in difficulties in handling and transporting, and the subsequent need for another reinforcing carrier tape that causes high costs.
These problems become more serious as the performances required for the package become higher along with demands for large-size packages for achieving multiple outputs and for finer pitches of wires.
The present invention has been devised so as to solve the above-mentioned problems with conventional methods, and its objective is to provide a tape carrier and a manufacturing method for a package and such a tape carrier, which can achieve miniaturization and cost reduction by placing a semiconductor element and a circuit part on both of the surfaces and which can also improve connection stability to an external device by minimizing a stress exerted at the time of the bending process.
In order to solve the above-mentioned problems, a tape carrier in accordance with the present invention, which entirely covers one of the surfaces of a semiconductor element, and is provided with a metal pattern which is connected to a connection terminal of the semiconductor element and an external device, is characterized in that the metal pattern is exposed to the surface opposite to the surface to which the semiconductor element is connected.
In accordance with the present invention, it is possible to connect a circuit element including a semiconductor element to the wiring pattern exposed to the surface on the side opposite to the surface to which the semiconductor element is connected, of the upper and lower two surfaces that the tape carrier has.
In the case of a conventional tape carrier which does not have a device hole and which entirely covers one of the surfaces of a semiconductor element, the surface on the side opposite to the surface to which the semiconductor element is connected is covered with a base film, and the metal pattern that is connected to inner and outer devices is not exposed. As compared with a tape carrier having a device hole, the tape carrier of this type has a disadvantage in that the assembling direction of the semiconductor element is limited to the face-down direction, although it has advantages such as low manufacturing costs. Therefore, the entire package circuit has to be formed on one surface of the tape carrier, resulting in limitation to the miniaturization of the tape carrier and the package.
In accordance with the above-mentioned invention, the metal pattern is exposed to the surface on the side opposite to the surface to which the semiconductor element is connected; therefore, a circuit element can be connected also to this surface, and a package circuit is constituted by using both of the surfaces of the tape carrier. With this arrangement, as compared with the conventional structure, it is possible to miniaturize the package, and also to cut costs. Moreover, with respect to a package having a predetermined size, it is possible to provide more margins in designing as compared with the conventional arrangement; thus, it becomes possible to widen the intervals between the parts, and consequently to revise the parts more easily.
Moreover, since the tape carrier of the present invention has no base film, the stress exerted at the time of bending of the tape carrier can be minimized by a value corresponding to the stress exerted due to the base film. Thus, in the case when a package is connected to an external device in a bent state, that is, for example, in the case when the package is connected to connection terminals of a liquid crystal device in a bent state, it is possible to reduce the occurrence of disconnection due to a bending stress exerted on the package. Since the bending stress of the package is small, it is possible to minimize the joining area to the connection terminals of a liquid crystal panel, etc., and consequently to further miniaturize the package.